A wide variety of engineering resins have been developed which are useful for the preparation of molded articles. The properties of the polymers are such that the resins may be used to replace metal in certain application. Heat resistance is a particularly critical property since in many applications the engineering resin must retain its mechanical properties and original form for prolonged periods at temperatures well above room temperature.
One type of engineering resin currently in widespread use is obtained by the copolymerization of styrene and maleic anhydride. These styrene/maleic anhydride copolymers contain from about 5 to 17 weight percent maleic anhydride and as a consequence have significantly higher heat resistance than polystyrene or acrylonitrile-butadiene-styrene (ABS) terpolymer. The maleic anhydride functionality also provides greatly improved adhesion to glass fiber, which is commonly used as a filler or reinforcement in the preparation of molded articles having high tensile strength and stiffness.
However, despite the generally satisfactory properties of the styrene/maleic anhydride copolymers, in certain applications it would be desirable to increase the heat resistance and tensile strength of these copolymers. These desired improvements in properties cannot be achieved simply by increasing the proportion of maleic anhydride because of the very high chain transfer activity of maleic anhydride and the marked tendency of the styrene/maleic anhydride system to form a low molecular weight alternating copolymer.
Accordingly, an object of the present invention is to provide thermoplastic resins having tensile strengths which are superior to comparable styrene/maleic anhydride copolymers.
A further object is to provide moldable plastics which have improved flexural strength relative to comparable styrene/maleic anhydride copolymers.
Still another object is to provide engineering resins having improved heat resistance.